Taylor Nelson Sofres has hit back as its potential suitor WPP, issuing a stinging statement this morning in response to "misleading statements disseminated by WPP".

The latest attack on WPP is part of an ongoing battle between the two firms since TNS announced that it had rejected WPP's latest £1 billion approach for the market research group yesterday morning.

Yesterday TNS told WPP to increase its £1 billion offer after the market research group rejected a third approach at 260p per share.

TNS began by attacking comments made by WPP that TNS had not provided the advertising giant with all the information it needed by saying, "The board believes that WPP has all the information required to value TNS".

"WPP continues to demand that TNS open its books and treat it fairly in terms of information disclosure, " continued TNS in a statement. "WPP has all the financial information on TNS that has been shared with GfK. This is more than is required to value a public company. TNS met for over four hours with WPP management and has answered numerous questions raised by WPP pertinent to the information provided. WPP is a competitor of TNS and TNS does not intend to share information with WPP that it has not shared with GfK."

In its statement, TNS also criticised a potential merger of WPP's market research firm Kantar with TNS. "WPP's Kantar-TNS proposition may offer scale but it does not fundamentally change the client offering," it said.

TNS added that WPP's claims about what the TNS share price would be without the merger talks "are misleading"

"WPP has stated that if TNS moved in line with the media sector, its share price would be significantly lower. TNS is the only UK quoted, independent market information company, operating in an industry that is demonstrating significant growth. Comparing TNS with a wider media index is misleading," TNS said, adding that the market research group's businesses are not dependent on advertising, unlike the majority of media companies. TNS continued its attack by adding in the statement that WPP's own share price performance has been poor, having fallen by 28 per cent at market close on 3 July 2008 since WPP's proposal for TNS on 13 May 2008.

"The board considers that it is important for all shareholders to have proper information on which to make judgments," said Mr Brydon.

Taylor Nelson Sofres also said that the administrative board of GfK Verein, GfK's majority shareholder, has voted in favour of the GfK-TNS merger.

TNS said that the latest vote of confidence meant that a vote of the GfK Verein at an extraordinary general meeting on 21 July "will be similarly successful".

Donald Brydon, the chairman of TNS, said: "We are very pleased that the Administrative Board of the Verein has voted positively in favour of the merger with TNS. We look forward to working with GfK to create an exciting new global force in market research that will be the envy of our peers."

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